His trial began at the District Court in Denpasar, Bali's capital, where prosecutors said Roberts violated anti-narcotics laws. If found guilty, he could face from four years to life in prison and a fine of at least $4,400.

The 35-year-old accountant earlier confessed to being a drug user but denied being a dealer.

Media reports said Roberts ran as a Liberal Democrat candidate for the Higgins seat in Melbourne in 2009 but was unsuccessful.

His social media accounts show he is a gym fan who regularly visits Bali and Thailand.

Indonesia has very strict drug laws and convicted traffickers can be executed by a firing squad. More than 150 people are on death row, mostly for drug crimes, and about a third of them are foreigners.

Eighteen people convicted of drug-related offenses have been executed under current President Joko "Jokowi" Widodo, who took office in October 2014.